Nanosensors

ABSTRACT

Electrical devices comprised of nanowires are described, along with methods of their manufacture and use. The nanowires can be nanotubes and nanowires. The surface of the nanowires may be selectively functionalized. Nanodetector devices are described.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/020,004, entitled “Nanosensors,” filed Dec. 11, 2001 now U.S. Pat.No. 7,129,554, which application claims priority under 35 U.S.C. §119(e)to commonly-owned, co-pending U.S. Provisional Patent Application Ser.Nos. 60/292,035, entitled “Nanowire and Nanotube Nanosensors,” filed May18, 2001 and 60/254,745, entitled “Nanowire and Nanotube Nanosensors,”filed Dec. 11, 2000, each of which is hereby incorporated by referencein its entirety.

FEDERALLY SPONSORED RESEARCH

This invention was sponsored by the National Science Foundation, GrantNo. 981226, and the Office of Naval Research, Contract No.N00014-00-1-0476. The government has certain rights in the invention.

FIELD OF INVENTION

The present invention relates generally to nanowires and nanoscaledevices and more particularly to a nanoscale device having a nanowire orfunctionalized nanowires for detecting the presence or absence of ananalyte suspected to be present in a sample, and method for using same.

BACKGROUND OF THE INVENTION

Nanowires are ideally suited for efficient transport of charge carriersand excitons, and thus are expected to be critical building blocks fornanoscale electronics and optoelectronics. Studies of electricaltransport in carbon nanotubes have led to the creation of field effecttransistors, single electron transistors, and rectifying junctions.

SUMMARY OF THE INVENTION

The present invention provides a series of nanoscale devices and methodsof use of the same.

In one aspect, the invention provides a nanoscale device. The device isdefined by a sample exposure region and a nanowire, wherein at least aportion of the nanowire is addressable by a sample in the sampleexposure region. In one embodiment, the device may further comprise adetector able to determine a property associated with the nanowire.

In another embodiment, the device is a sample cassette comprising asample exposure region and a nanowire. At least a portion of thenanowire is addressable by a sample in the sample exposure region, andthe sample cassette is operatively connectable to a detector apparatusthat is able to determine a property associated with the nanowire.

In another embodiment, the device is a sensor comprising at least onenanowire and means for measuring a change in a property of the at leastone nanowire.

In another embodiment, the device comprises functionalized nanowirescomprising a core region of a bulk nanowire and an outer region offunctional moieties.

Another aspect of the invention provides a method involving determininga property change of a nanowire when the nanowire is contacted with asample suspected of containing an analyte.

Another method involves measuring a change in a property associated witha nanowire, when the nanowire is contacted with a sample having a volumeof less than about 10 microliters.

Another method involves determining the presence or quantity of ananalyte in a sample suspected of containing an analyte. A change in aproperty of a nanowire resulting from contacting the nanowire and thesample is measured

Another method for detecting an analyte comprises contacting a nanowirewith a sample and determining a property associated with the nanowire. Achange in the property of the nanowire indicates the presence orquantity of the analyte the sample.

Another method comprises contacting an electrical conductor with asample and determining the presence or quantity of an analyte in thesample by measuring a change in a property of the conductor resultantfrom the contact. Less than ten molecules of the analyte contribute tothe change in the property.

Another aspect of the invention provides an integrated multifunctionarysystem comprising a nanowire sensor, a signal interpreter, signalfeedback component and an intervention delivery component.

Another aspect of the invention provides a nanowire sensor devicecomprising a semiconductor nanowire and a binding partner having aspecificity for a selected moiety. The nanowire has an exterior surfaceformed thereon to form a gate electrode. The nanowire also has a firstend in electrical contact with a conductor to form a source electrodeand a second end in contact with a conductor to form a drain electrode.

Another aspect of the invention provides an analyte-gated field effecttransistor having a predetermined current-voltage characteristic andadapted for use as a chemical or biological sensor. The field effecttransistor comprises a substrate formed of a first insulating material,a source electrode, a drain electrode, and a semiconductor nanowiredisposed between the source and drain electrodes, and ananalyte-specific minding partner disposed on a surface of the nanowire.A binding event occurring between a target analyte and the bindingpartner causes a detectable change in a current-voltage characteristicof the field effect transistor. Another aspect of the invention providesan array of at least 100 analyte gate field effect transistors.

Other advantages, novel features, and objects of the invention willbecome apparent from the following detailed description of non-limitingembodiments of the invention when considered in conjunction with theaccompanying drawings, which are schematic and which are not intended tobe drawn to scale. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures is represented by asingle numeral. For purposes of clarity, not every component is labeledin every figure, nor is every component of each embodiment of theinvention shown where illustration is not necessary to allow those ofordinary skill in the art to understand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates, schematically, a nanoscale detector device.

FIG. 1 b illustrates, schematically, a nanoscale detector device with aparallel array of nanowires.

FIG. 2 a illustrates, schematically, a nanoscale detector device inwhich a nanowire has been modified with a binding agent for detection ofa complementary binding partner.

FIG. 2 b illustrates, schematically, the nanoscale detector device ofFIG. 2 a, in which a complementary binding partner is fastened to thebinding agent.

FIG. 3 a is a low resolution scanning electron micrograph of a singlesilicon nanowire connected to two metal electrodes.

FIG. 3 b is a high resolution scanning electron micrograph of a singlesilicon nanowire device connected to two metal electrodes.

FIG. 4 a shows schematically another embodiment of a nanoscale sensorhaving a backgate.

FIG. 4 b shows conductance vs. time with various backgate voltages.

FIG. 4 c shows conductance vs. backgate voltage.

FIG. 5 a shows conductance for a single silicon nanowire as a functionof pH.

FIG. 5 b shows conductance versus pH for a single silicon nanowire thathas been modified to expose amine groups at the surface.

FIG. 6 shows conductance versus time for a silicon nanowire with asurface modified with oligonucleotide agents.

FIG. 7 is an atomic force microscopy image of a typical single wallnanotube detector device.

FIG. 8 a shows current-voltage (I-V) measurements for a single-walledcarbon nanotube device in air.

FIG. 8 b shows current-voltage (I-V) measurements for the single-walledcarbon nanotube device of FIG. 8 a in NaCl.

FIG. 8 c shows current-voltage (I-V) measurements for a single-walledcarbon nanotube device, of FIG. 8 b in CrClx.

FIG. 9 a shows the conductance of nanosensors with hydroxyl surfacegroups when exposed to pH levels from 2 to 9.

FIG. 9 b shows the conductance of nanosensors modified with amine groupswhen exposed to pH levels from 2 to 9.

FIG. 9 c show the relative conductance of the nanosensors with changesin pH levels.

FIG. 10 a shows the conductance of a SiNW modified with BSA Biotin, asit is exposed first to a blank buffer solution, and then to a solutioncontaining 250 nM Streptavidin.

FIG. 10 b shows the conductance of a SiNW modified with BSA Biotin, asit is exposed first to a blank buffer solution, and then to a solutioncontaining 25 pM Streptavidin.

FIG. 10 c shows the conductance of a bare SiNW as it is exposed first toa blank buffer solution, and then to a solution containing Streptavidin.

FIG. 10 d shows the conductance of a SiNW modified with BSA Biotin, asit is exposed to a buffer solution, and then to a solution containingd-biotin Streptavidin.

FIG. 10 e shows the conductance of a Biotin modified nanosensor exposedto a blank buffer solution, then to a solution containing Streptavidin,and then again to a blank buffer solution.

FIG. 10 f shows the conductance of a bare SiNW as it is alternatelyexposed to a buffer solution and a solution containing streptavidin.

FIG. 11 a shows the conductance of a BSA-Biotin modified SiNW as it isexposed first to a blank buffer solution, then to a solution containingAntibiotin.

FIG. 11 b shows the conductance of a bare SiNW during contact with abuffer solution and then a solution containing Antibiotin.

FIG. 11 c shows the conductance of a BSA-Biotin modified SiNW duringexposure to a buffer, other IgG type antibodies, and then Antibiotin.

FIG. 12 a shows the conductance of an amine modified SiNW whenalternately exposed to a blank buffer solution and a solution containing1 mM Cu(II).

FIG. 12 b shows the conductance of the amine modified SiNW is exposed toconcentrations of Cu(II) from 0.1 mM to 1 mM.

FIG. 12 c shows the conductance verses Cu(II) concentration.

FIG. 12 d shows conductance of an unmodified SiNW when exposed first toa blank buffer solution and then to 1 mM Cu(II).

FIG. 12 e shows conductance of an amine-modified SiNW when exposed firstto a blank buffer solution and then to 1 mM Cu(II)-EDTA.

FIG. 13 a shows the conductance of a calmodulin-modified siliconnanowire exposed to a buffer solution and then to a solution containingcalcium ions.

FIG. 13 b shows the conductance of a bare silicon nanowire exposed to abuffer solution and then to a solution containing calcium ions.

FIG. 14 a shows a calculation of sensitivity for detecting up to 5charges compared with doping concentration and nanowire diameter.

FIG. 14 b shows a calculation of the threshold doping density comparedto nanowire diameter for detecting a single charge.

FIG. 15 a is a schematic view of an InP nanowire.

FIG. 15 b shows the change in luminescence of a nanowire of FIG. 15 aover time as pH varies.

FIG. 16 a depicts one embodiment of a nanowire sensor, specifically achemical or ligand-gated Field Effects Transistor (FET).

FIG. 16 b show another view of the nanowire of FIG. 16 a.

FIG. 16 c illustrates the nanowire of FIG. 16 a with moieties at thesurface.

FIG. 16 d illustrates the nanowire of FIG. 16 c with a depletion region.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a series of techniques and devicesinvolving nanowires. One aspect of the invention provides functionalizednanowires. While many uses for nanowires have been developed, many moredifferent and important uses are facilitated by the present inventionwhere the nanowires are functionalized at their surface, or in closeproximity to their surface. In one particular case, functionalization(e.g., with a reaction entity), either uniformly or non-uniformly,permits interaction of the functionalized nanowire with variousentities, such as molecular entities, and the interaction induces achange in a property of the functionalized nanowire, which provides amechanism for a nanoscale sensoring device. Another aspect of theinvention is a sensor that comprises a nanowire, or a functionalizednanowire. Various aspects of the invention are described below ingreater detail.

As used herein, a “nanowire” is an elongated nanoscale semiconductorwhich, at any point along its length, has at least one cross-sectionaldimension and, in some embodiments, two orthogonal cross-sectionaldimensions less than 500 nanometers, preferably less than 200nanometers, more preferably less than 150 nanometers, still morepreferably less than 100 nanometers, even more preferably less than 70,still more preferably less than 50 nanometers, even more preferably lessthan 20 nanometers, still more preferably less than 10 nanometers, andeven less than 5 nanometers. In other embodiments, the cross-sectionaldimension can be less than 2 nanometers or 1 nanometer. In one set ofembodiments the nanowire has at least one cross-sectional dimensionranging from 0.5 nanometers to 200 nanometers. Where nanowires aredescribed having a core and an outer region, the above dimensions relateto those of the core. The cross-section of the elongated semiconductormay have any arbitrary shape, including, but not limited to, circular,square, rectangular, elliptical and tubular. Regular and irregularshapes are included. A non-limiting list of examples of materials fromwhich nanowires of the invention can be made appears below. Nanotubesare a class of nanowires that find use in the invention and, in oneembodiment, devices of the invention include wires of scale commensuratewith nanotubes. As used herein, a “nanotube” is a nanowire that has ahollowed-out core, and includes those nanotubes know to those ofordinary skill in the art. A “non-nanotube nanowire” is any nanowirethat is not a nanotube. In one set of embodiments of the invention, anon-nanotube nanowire having an unmodified surface (not including anauxiliary reaction entity not inherent in the nanotube in theenvironment in which it is positioned) is used in any arrangement of theinvention described herein in which a nanowire or nanotube can be used.A “wire” refers to any material having a conductivity at least that of asemiconductor or metal. For example, the term “electrically conductive”or a “conductor” or an “electrical conductor” when used with referenceto a “conducting” wire or a nanowire refers to the ability of that wireto pass charge through itself. Preferred electrically conductivematerials have a resistivity lower than about 10⁻³, more preferablylower than about 10⁻⁴, and most preferably lower than about 10⁻⁶ or 10⁻⁷ohm-meters.

The invention provides a nanowire or nanowires preferably forming partof a system constructed and arranged to determine an analyte in a sampleto which the nanowire(s) is exposed. “Determine”, in this context, meansto determine the quantity and/or presence of the analyte in the sample.Presence of the analyte can be determined by determining a change in acharacteristic in the nanowire, typically an electrical characteristicor an optical characteristic. E.g. an analyte causes a detectable changein electrical conductivity of the nanowire or optical properties. In oneembodiment, the nanowire includes, inherently, the ability to determinethe analyte. The nanowire may be functionalized, i.e. comprising surfacefunctional moieties, to which the analytes binds and induces ameasurable property change to the nanowire. The binding events can bespecific or non-specific. The functional moieties may include simplegroups, selected from the groups including, but not limited to, —OH,—CHO, —COOH, —SO₃H, —CN, —NH₂, —SH, —COSH, COOR, halide; biomolecularentities including, but not limited to, amino acids, proteins, sugars,DNA, antibodies, antigens, and enzymes; grafted polymer chains withchain length less than the diameter of the nanowire core, selected froma group of polymers including, but not limited to, polyamide, polyester,polyimide, polyacrylic; a thin coating covering the surface of thenanowire core, including, but not limited to, the following groups ofmaterials: metals, semiconductors, and insulators, which may be ametallic element, an oxide, an sulfide, a nitride, a selenide, a polymerand a polymer gel. In another embodiment, the invention provides ananowire and a reaction entity with which the analyte interacts,positioned in relation to the nanowire such that the analyte can bedetermined by determining a change in a characteristic of the nanowire.

The term “reaction entity” refers to any entity that can interact withan analyte in such a manner to cause a detectable change in a propertyof a nanowire. The reaction entity may enhance the interaction betweenthe nanowire and the analyte, or generate a new chemical species thathas a higher affinity to the nanowire, or to enrich the analyte aroundthe nanowire. The reaction entity can comprise a binding partner towhich the analyte binds. The reaction entity, when a binding partner,can comprise a specific binding partner of the analyte. For example, thereaction entity may be a nucleic acid, an antibody, a sugar, acarbohydrate or a protein. Alternatively, the reaction entity may be apolymer, catalyst, or a quantum dot. A reaction entity that is acatalyst can catalyze a reaction involving the analyte, resulting in aproduct that causes a detectable change in the nanowire, e.g. viabinding to an auxiliary binding partner of the product electricallycoupled to the nanowire. Another exemplary reaction entity is a reactantthat reacts with the analyte, producing a product that can cause adetectable change in the nanowire. The reaction entity can comprise acoating on the nanowire, e.g. a coating of a polymer that recognizesmolecules in, e.g., a gaseous sample, causing a change in conductivityof the polymer which, in turn, causes a detectable change in thenanowire.

The term “quantum dot” is known to those of ordinary skill in the art,and generally refers to semiconductor or metal nanoparticles that absorblight and quickly re-emit light in a different color depending on thesize of the dot. For example, a 2 nanometer quantum dot emits greenlight, while a 5 nanometer quantum dot emits red light. Cadmium Selenidequantum dot nanocrystals are available from Quantum Dot Corporation ofHayward, Calif.

The term “binding partner” refers to a molecule that can undergo bindingwith a particular analyte, or “binding partner” thereof, and includesspecific, semi-specific, and non-specific binding partners as known tothose of ordinary skill in the art. E.g., Protein A is usually regardedas a “non-specific” or semi-specific binder. The term “specificallybinds”, when referring to a binding partner (e.g., protein, nucleicacid, antibody, etc.), refers to a reaction that is determinative of thepresence and/or identity of one or other member of the binding pair in amixture of heterogeneous molecules (e.g., proteins and other biologics).Thus, for example, in the case of a receptor/ligand binding pair theligand would specifically and/or preferentially select its receptor froma complex mixture of molecules, or vice versa. An enzyme wouldspecifically bind to its substrate, a nucleic acid would specificallybind to its complement, an antibody would specifically bind to itsantigen. Other examples include, nucleic acids that specifically bind(hybridize) to their complement, antibodies specifically bind to theirantigen, and the like.

The binding may be by one or more of a variety of mechanisms including,but not limited to ionic interactions, and/or covalent interactions,and/or hydrophobic interactions, and/or van der Waals interactions, etc.

The term “fluid” is defined as a substance that tends to flow and toconform to the outline of its container: Typically fluids are materialsthat are unable to withstand a static shear stress. When a shear stressis applied to a fluid it experiences a continuing and permanentdistortion. Typical fluids include liquids and gasses, but may alsoinclude free flowing solid particles.

The term “sample” refers to any cell, tissue, or fluid from a biologicalsource (a “biological sample”), or any other medium, biological ornon-biological, that can be evaluated in accordance with the inventionincluding, such as serum or water. A sample includes, but is not limitedto, a biological sample drawn from an organism (e.g. a human, anon-human mammal, an invertebrate, a plant, a fungus, an algae, abacteria, a virus, etc.), a sample drawn from food designed for humanconsumption, a sample including food designed for animal consumptionsuch as livestock feed, milk, an organ donation sample, a sample ofblood destined for a blood supply, a sample from a water supply, or thelike. One example of a sample is a sample drawn from a human or animalto determine the presence or absence of a specific nucleic acidsequence.

A “sample suspected of containing” a particular component means a samplewith respect to which the content of the component is unknown. Forexample, a fluid sample from a human suspected of having a disease, suchas a neurodegenerative disease or a non-neurodegenerative disease, butnot known to have the disease, defines a sample suspected of containingneurodegenerative disease. “Sample” in this context includesnaturally-occurring samples, such as physiological samples from humansor other animals, samples from food, livestock feed, etc. Typicalsamples taken from humans or other animals include tissue biopsies,cells, whole blood, serum or other blood fractions, urine, ocular fluid,saliva, cerebro-spinal fluid, fluid or other samples from tonsils, lymphnodes, needle biopsies, etc.

The term “electrically coupled” when used with reference to a nanowireand an analyte, or other moiety such as a reaction entity, refers to anassociation between any of the analyte, other moiety, and the nanowiresuch that electrons can move from one to the other, or in which a changein an electrical characteristic of one can be determined by the other.This can include electron flow between these entities, or a change in astate of charge, oxidation, or the like that can be determined by thenanowire. As examples, electrical coupling can include direct covalentlinkage between the analyte or other moiety and the nanowire, indirectcovalent coupling (e.g. via a linker), direct or indirect ionic bondingbetween the analyte (or other moiety) and the nanowire, or other bonding(e.g. hydrophobic bonding). In some cases, no actual bonding may berequired and the analyte or other moiety may simply be contacted withthe nanowire surface. There also need not necessarily be any contactbetween the nanowire and the analyte or other moiety where the nanowireis sufficiently close to the analyte to permit electron tunnelingbetween the analyte and the nanowire.

The terms “polypeptide”, “peptide” and “protein” are usedinterchangeably herein to refer to a polymer of amino acid residues. Theterms apply to amino acid polymers in which one or more amino acidresidue is an artificial chemical analogue of a corresponding naturallyoccurring amino acid, as well as to naturally occurring amino acidpolymers. The term also includes variants on the traditional peptidelinkage joining the amino acids making up the polypeptide.

The terms “nucleic acid” or “oligonucleotide” or grammatical equivalentsherein refer to at least two nucleotides covalently linked together. Anucleic acid of the present invention is preferably single-stranded ordouble stranded and will generally contain phosphodiester bonds,although in some cases, as outlined below, nucleic acid analogs areincluded that may have alternate backbones, comprising, for example,phosphoramide (Beaucage et al. (1993) Tetrahedron 49(10):1925) andreferences therein; Letsinger (1970) J. Org. Chem. 35:3800; Sprinzl etal. (1977) Eur. J. Biochem. 81: 579; Letsinger et al. (1986) Nucl. AcidsRes. 14: 3487; Sawai et al. (1984) Chem. Lett. 805, Letsinger et al.(1988) J. Am. Chem. Soc. 110: 4470; and Pauwels et al. (1986) ChemicaScripta 26: 1419), phosphorothioate (Mag et al. (1991) Nucleic AcidsRes. 19:1437; and U.S. Pat. No. 5,644,048), phosphorodithioate (Briu etal. (1989) J. Am. Chem. Soc. 111:2321, O-methylphophoroamidite linkages(see Eckstein, Oligonucleotides and Analogues: A Practical Approach,Oxford University Press), and peptide nucleic acid backbones andlinkages (see Egholm (1992) J. Am. Chem. Soc. 114:1895; Meier et al.(1992) Chem. Int. Ed. Engl. 31: 1008; Nielsen (1993) Nature, 365: 566;Carlsson et al. (1996) Nature 380: 207). Other analog nucleic acidsinclude those with positive backbones (Denpcy et al. (1995) Proc. Natl.Acad. Sci. USA 92: 6097; non-ionic backbones (U.S. Pat. Nos. 5,386,023,5,637,684, 5,602,240, 5,216,141 and 4,469,863; Angew. (1991) Chem. Intl.Ed. English 30: 423; Letsinger et al. (1988) J. Am. Chem. Soc. 110:4470;Letsinger et al. (1994) Nucleoside & Nucleotide 13:1597; Chapters 2 and3, ASC Symposium Series 580, “Carbohydrate Modifications in AntisenseResearch”, Ed. Y. S. Sanghui and P. Dan Cook; Mesmaeker et al. (1994),Bioorganic & Medicinal Chem. Lett. 4: 395; Jeffs et al. (1994) J.Biomolecular NMR 34:17; Tetrahedron Lett. 37:743 (1996)) and non-ribosebackbones, including those described in U.S. Pat. Nos. 5,235,033 and5,034,506, and Chapters 6 and 7, ASC Symposium Series 580, CarbohydrateModifications in Antisense Research, Ed. Y. S. Sanghui and P. Dan Cook.Nucleic acids containing one or more carbocyclic sugars are alsoincluded within the definition of nucleic acids (see Jenkins et al.(1995), Chem. Soc. Rev. pp. 169-176). Several nucleic acid analogs aredescribed in Rawls, C & E News Jun. 2, 1997 page 35. These modificationsof the ribose-phosphate backbone may be done to facilitate the additionof additional moieties such as labels, or to increase the stability andhalf-life of such molecules in physiological environments.

As used herein, an “antibody” refers to a protein or glycoproteinconsisting of one or more polypeptides substantially encoded byimmunoglobulin genes or fragments of immunoglobulin genes. Therecognized immunoglobulin genes include the kappa, lambda, alpha, gamma,delta, epsilon and mu constant region genes, as well as myriadimmunoglobulin variable region genes. Light chains are classified aseither kappa or lambda. Heavy chains are classified as gamma, mu, alpha,delta, or epsilon, which in turn define the immunoglobulin classes, IgG,IgM, IgA, IgD and IgE, respectively. A typical immunoglobulin (antibody)structural unit is known to comprise a tetramer. Each tetramer iscomposed of two identical pairs of polypeptide chains, each pair havingone “light” (about 25 kD) and one “heavy” chain (about 50-70 kD). TheN-terminus of each chain defines a variable region of about 100 to 110or more amino acids primarily responsible for antigen recognition. Theterms variable light chain (VL) and variable heavy chain (VH) refer tothese light and heavy chains respectively.

Antibodies exist as intact immunoglobulins or as a number of wellcharacterized fragments produced by digestion with various peptidases.Thus, for example, pepsin digests an antibody below (i.e. toward the Fcdomain) the disulfide linkages in the hinge region to produce F(ab)′2, adimer of Fab which itself is a light chain joined to V_(H)-C_(H)1 by adisulfide bond. The F(ab)′2 may be reduced under mild conditions tobreak the disulfide linkage in the hinge region thereby converting the(Fab′)2 dimer into an Fab′ monomer. The Fab′ monomer is essentially aFab with part of the hinge region (see, Paul (1993) FundamentalImmunology, Raven Press, N.Y. for a more detailed description of otherantibody fragments). While various antibody fragments are defined interms of the digestion of an intact antibody, one of skill willappreciate that such fragments may be synthesized de novo eitherchemically, by utilizing recombinant DNA methodology, or by “phagedisplay” methods (see, e.g., Vaughan et al. (1996) Nature Biotechnology,14(3): 309-314, and PCT/US96/10287). Preferred antibodies include singlechain antibodies, e.g., single chain Fv (scFv) antibodies in which avariable heavy and a variable light chain are joined together (directlyor through a peptide linker) to form a continuous polypeptide.

One aspect of the invention involves a sensing element, which can be anelectronic sensing element, and a nanowire able to detect the presence,or absence, of an analyte in a sample (e.g. a fluid sample) containing,or suspected of containing, the analyte. Nanoscale sensors of theinvention may be used, for example, in chemical applications to detectpH or the presence of metal ions; in biological applications to detect aprotein, nucleic acid (e.g. DNA, RNA, etc.), a sugar or carbohydrate,and/or metal ions; and in environmental applications to detect pH, metalions, or other analytes of interest.

Another aspect of the present invention provides an article comprising ananowire and a detector constructed and arranged to determine a changein an electrical property of the nanowire. At least a portion of thenanowire is addressable by a sample containing, or suspected ofcontaining, an analyte. The phrase “addressable by a fluid” is definedas the ability of the fluid to be positioned relative to the nanowire sothat an analyte suspected of being in the fluid is able to interact withthe nanowire. The fluid may be proximate to or in contact with thenanowire.

In all of the illustrative embodiments described herein, any nanowirecan be used, including carbon nanotubes, nanorods, nanowires, organicand inorganic conductive and semiconducting polymers, and the likeunless otherwise specified. Other conductive or semiconducting elementsthat may not be molecular wires, but are of various smallnanoscopic-scale dimension, also can be used in some instances, e.g.inorganic structures such as main group and metal atom-based wire-likesilicon, transition metal-containing wires, gallium arsenide, galliumnitride, indium phosphide, germanium, cadmium selenide structures. Awide variety of these and other nanowires can be grown on and/or appliedto surfaces in patterns useful for electronic devices in a mannersimilar to techniques described herein involving nanowires, withoutundue experimentation. The nanowires should be able to be formed of atleast one micron, preferably at least three microns, more preferably atleast five microns, and more preferably still at least ten or twentymicrons in length, and preferably are less than about 100 nanometers,more preferably less than about 75 nanometers, and more preferably lessthan about 50 nanometers, and more preferably still less than about 25nanometers in thickness (height and width). The wires should have anaspect ratio (length to thickness) of at least about 2:1, preferablygreater than about 10:1, and more preferably greater than about 1000:1.A preferred nanowire for use in devices of the invention can be either ananotube or a nanowire. Nanotubes (e.g. carbon nanotubes) are hollow.Nanowires (e.g. silicon nanowires) are solid.

Whether nanotubes or nanowires are selected, the criteria for selectionof nanowires and other conductors or semiconductors for use in theinvention are based, in some instances, mainly upon whether the nanowireitself is able to interact with an analyte, or whether the appropriatereaction entity, e.g. binding partner, can be easily attached to thesurface of the nanowire, or the appropriate reaction entity, e.g.binding partner, is near the surface of the nanowire. Selection ofsuitable conductors or semiconductors, including nanowires, will beapparent and readily reproducible by those of ordinary skill in the artwith the benefit of the present disclosure.

Nanotubes that may be used in the present invention includesingle-walled nanotubes (SWNTs) that exhibit unique electronic, andchemical properties that are particularly suitable for molecularelectronics. Structurally, SWNTs are formed of a single graphene sheetrolled into a seamless tube with a diameter on the order of about 0.5 nmto about 5 nm and a length that can exceed about 10 microns. Dependingon diameter and helicity, SWNTs can behave as one-dimensional metals orsemiconductor and are currently available as a mixture of metallic andsemiconducting nanotubes. Methods of manufacture of nanotubes, includingSWNTs, and characterization are known. Methods of selectivefunctionalization on the ends and/or sides of nanotubes also are known,and the present invention makes use of these capabilities for molecularelectronics. The basic structural/electronic properties of nanotubes canbe used to create connections or input/output signals, and nanotubeshave a size consistent with molecular scale architecture.

Preferred nanowires of the present invention are individual nanowires.As used herein, “individual nanowires” means a nanowire free of contactwith another nanowire (but not excluding contact of a type that may bedesired between individual nanowires in a crossbar array). For example,typical individual nanowire can have a thickness as small as about 0.5nm. This is in contrast to nanowires produced primarily by laservaporization techniques that produce high-quality materials, butmaterials formed as ropes having diameters of about 2 to about 50nanometers or more and containing many individual nanowires (see, forexample, Thess, et al., “Crystalline Ropes of Metallic Carbon Nanotubes”Science 273, 483-486 (1996), incorporated herein by reference). Whilenanowire ropes can be used in the invention, individual nanowires arepreferred.

The invention may utilize metal-catalyzed CVD to synthesize high qualityindividual nanowires such as nanotubes for molecular electronics. CVDsynthetic procedures needed to prepare individual wires directly onsurfaces and in bulk form are known, and can readily be carried out bythose of ordinary skill in the art. See, for example, Kong, et al.,“Synthesis of Individual Single-Walled Carbon Nanotubes on PatternedSilicon Wafers”, Nature 395, 878-881 (1998); Kong, et al., “ChemicalVapor Deposition of Methane for Single-Walled Carbon Nanotubes” Chem.Phys. Lett. 292, 567-574 (1998), both incorporated herein by reference.Nanowires may also be grown through laser catalytic growth. See, forexample, Morales et al. “A Laser Ablation Method for the Synthesis ofCrystalline Semiconductor Nanowires” Science 279, 208-211 (1998),incorporated herein by reference.

Alternatively, the nanowire may comprise a semiconductor that is dopedwith an appropriate dopant to create an n-type or p-type semiconductoras desired. For example, silicon may be doped with boron, aluminum,phosphorous, or arsenic. Laser catalytic growth may be used to introducecontrollably the dopants during the vapor phase growth of siliconnanowires.

Controlled doping of nanowires can be carried out to form, e.g., n-typeor p-type semiconductors. In various embodiments, this inventioninvolves controlled doping of semiconductors selected from among indiumphosphide, gallium arsenide, gallium nitride, cadmium selenide, and zincselenide. Dopants including, but not limited to, zinc, cadmium, ormagnesium can be used to form p-type semiconductors in this set ofembodiments, and dopants including, but not limited to, tellurium,sulfur, selenium, or germanium can be used as dopants to form n-typesemiconductors from these materials. These materials define direct bandgap semiconductor materials and these and doped silicon are well knownto those of ordinary skill in the art. The present inventioncontemplates use of any doped silicon or direct band gap semiconductormaterials for a variety of uses.

As examples of nanowire growth, placement, and doping, SiNWs (elongatednanoscale semiconductors) may be synthesized using laser assistedcatalytic growth (LCG). As shown in FIGS. 2 and 3, laser vaporization ofa composite target that is composed of a desired material (e.g. InP) anda catalytic material (e.g. Au) creates a hot, dense vapor which quicklycondenses into liquid nanoclusters through collision with the buffergas. Growth begins when the liquid nanoclusters become supersaturatedwith the desired phase and continues as long as the reactant isavailable. Growth terminates when the nanowires pass out of the hotreaction zone or when the temperature is turned down. Au is generallyused as catalyst for growing a wide range of elongated nanoscalesemiconductors. However, The catalyst is not limited to Au only. A widerage of materials such as (Ag, Cu, Zn, Cd, Fe, Ni, Co . . . ) can beused as the catalyst. Generally, any metal that can form an alloy withthe desired semiconductor material, but doesn't form more stablecompound than with the elements of the desired semiconductor can be usedas the catalyst. The buffer gas can be Ar, N2, and others inert gases.Sometimes, a mixture of H2 and buffer gas is used to avoid undesiredoxidation by residue oxygen. Reactive gas can also be introduced whendesired (e.g. ammonia for GaN).The key point of this process is laserablation generates liquid nanoclusters that subsequently define the sizeand direct the growth direction of the crystalline nanowires. Thediameters of the resulting nanowires are determined by the size of thecatalyst cluster, which in turn can be varied by controlling the growthconditions (e.g. background pressure, temperature, flow rate . . . ).For example, lower pressure generally produces nanowires with smallerdiameters. Further diameter control can be done by using uniformdiameter catalytic clusters.

With same basic principle as LCG, if uniform diameter nanoclusters (lessthan 10-20% variation depending on how uniform the nanoclusters are) areused as the catalytic cluster, nanowires with uniform size (diameter)distribution can be produced, where the diameter of the nanowires isdetermined by the size of the catalytic clusters, as illustrated in FIG.4. By controlling the growth time, nanowires with different lengths canbe grown.

With LCG, nanowires can be flexibly doped by introducing one or moredopants into the composite target (e.g., Ge for n-type doping of InP).The doping concentration can be controlled by controlling the relativeamount of doping element, typically 0-20%, introduced in the compositetarget.

Laser ablation may be used as the way to generate the catalytic clustersand vapor phase reactant for growth of nanowires and other relatedelongated nanoscale structures, but fabrication is not limited to laserablation. Many ways can be used to generate vapor phase and catalyticclusters for nanowire growth (e.g. thermal evaporation).

Another technique that may be used to grow nanowires is catalyticchemical vapor deposition (C-CVD). C-CVD utilizes the same basicprinciples as LCG, except that in the C-CVD method, the reactantmolecules (e.g., silane and the dopant) are from vapor phase molecules(as opposed to vapor source from laser vaporization.

In C-CVD, nanowires can be doped by introducing the doping element intothe vapor phase reactant (e.g. diborane and phosphane for p-type andn-type doped nanowire). The doping concentration can be controlled bycontrolling the relative amount of the doping element introduced in thecomposite target. It is not necessary to obtain elongated nanoscalesemiconductors with the same doping ratio as that in the gas reactant.However, by controlling the growth conditions (e.g. temperature,pressure . . . ), nanowires with same doping concentration can bereproduced. And the doping concentration can be varied over a largerange by simply varying the ratio of gas reactant (e.g. 1 ppm-10%).

There are several other techniques that may be used to grow elongatednanoscale semiconductors such as nanowires. For example, nanowires ofany of a variety of materials can be grown directly from vapor phasethrough a vapor-solid process. Also, nanowires can also be produced bydeposition on the edge of surface steps, or other types of patternedsurfaces, as shown in FIG. 5. Further, nanowires can be grown by vapordeposition in/on any general elongated template, for example, as shownin FIG. 6. The porous membrane can be porous silicon, anodic alumina ordiblock copolymer and any other similar structure. The natural fiber canbe DNA molecules, protein molecules carbon nanotubes, any otherelongated structures. For all the above described techniques, the sourcematerials can be came from a solution phase rather than a vapor phase.While in solution phase, the template can also be column micelles formedby surfactant molecules in addition to the templates described above.

Using one or more of the above techniques, elongated nanoscalesemiconductors, including semiconductor nanowires and dopedsemiconductor nanowires, can be grown. Such bulk-doped semiconductorsmay include various combinations of materials, including semiconductorsand dopants. The following are non-comprehensive lists of suchmaterials. Other materials may be used. Such materials include, but arenot limited to:

Elemental Semiconductors:

Si, Ge, Sn, Se, Te, B, Diamond, P

Solid Solution of Elemental Semiconductors:

B—C, B—P(BP6), B—Si, Si—C, Si—Ge, Si—Sn, Ge—Sn

IV-IV Group Semiconductors:

SiC

III-V Semiconductors:

BN/BP/BAs, AlN/AlP/AlAs/AlSb, GaN/GaP/GaAs/GaSb, InN/InP/InAs/InSb,

Alloys of III-V Group:

any combination of two or more of the above compound (e.g.: AlGaN,GaPAs, InPAs, GaInN, AlGaInN, GaInAsP . . . )

II-VI Semiconductors:

ZnO/ZnS/ZnSe/ZnTe, CdS/CdSe/CdTe, HgS/HgSe/HgTe, BeS/BeSe/BeTe/MgS/MgSe

Alloys of II-VI Group: any combination of two or more of the abovecompound (e.g.: (ZnCd)Se, Zn(SSe) . . . )

Alloy of II-VI and III-V Semiconductors:

combination of any one II-VI and one III-V compounds, e.g.(GaAs)_(x)(ZnS)_(1-x)

IV-VI Semiconductors:

GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe

I-VII Semiconductors:

CuF, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI

Other Semiconductor Compounds:

II-IV-V₂: BeSiN2, CaCN2, ZnGeP2, CdSnAs2, ZnSnSb2 . . .

I-IV₂-V₃: CuGeP3, CuSi2P3 . . .

I-III-VI₂: Cu, Ag)(Al, Ga, In, Tl, Fe)(S, Se, Te)2

IV₃-V₄: Si3N4, Ge3N4 . . .

III₂-VI₃: Al2O3, (Al, Ga, In)2(S, Se, Te)3 . . .

III₂-IV-VI: Al2CO . . .

For Group IV semiconductor materials, a p-type dopant may be selectedfrom Group III, and an n-type dopant may be selected from Group V. Forsilicon semiconductor materials, a p-type dopant may be selected fromthe group consisting of B, Al and In, and an n-type dopant may beselected from the group consisting of P, As and Sb. For Group III-Vsemiconductor materials, a p-type dopant may be selected from Group II,including Mg, Zn, Cd and Hg, or Group IV, including C and Si. An n-typedopant may be selected from the group consisting of Si, Ge, Sn, S, Seand Te. It will be understood that the invention is not limited to thesedopants.

Nanowires may be either grown in place or deposited after growth.Assembly, or controlled placement of nanowires on surfaces after growthcan be carried out by aligning nanowires using an electrical field. Anelectrical field is generated between electrodes, nanowires arepositioned between the electrodes (optionally flowed into a regionbetween the electrodes in a suspending fluid), and will align in theelectrical field and thereby can be made to span the distance betweenand contact each of the electrodes.

In another arrangement individual contact points are arranged inopposing relation to each other, the individual contact points beingtapered to form a point directed towards each other. An electric fieldgenerated between such points will attract a single nanowire spanningthe distance between, and contacting each of, the electrodes. In thisway individual nanowires can readily be assembled between individualpairs of electrical contacts. Crossed-wire arrangements, includingmultiple crossings (multiple parallel wires in a first direction crossedby multiple parallel wires in a perpendicular or approximatelyperpendicular second direction) can readily be formed by firstpositioning contact points (electrodes) at locations where opposite endsof the crossed wires desirably will lie. Electrodes, or contact points,can be fabricated via typical microfabrication techniques.

These assembly techniques can be substituted by, or complemented with, apositioning arrangement involving positioning a fluid flow directingapparatus to direct fluid containing suspended nanowires toward and inthe direction of alignment with locations at which nanowires aredesirably positioned.

Another arrangement involves forming surfaces including regions thatselectively attract nanowires surrounded by regions that do notselectively attract them. For example, —NH₂ can be presented in aparticular pattern at a surface, and that pattern will attract nanowiresor nanotubes having surface functionality attractive to amines. Surfacescan be patterned using known techniques such as electron-beampatterning, “soft-lithography” such as that described in InternationalPatent Publication No. WO 96/29629, published Jul. 26, 1996, or U.S.Pat. No. 5,512,131, issued Apr. 30, 1996, each of which is incorporatedherein by reference.

A technique is also known to direct the assembly of a pre-formednanowire onto a chemically patterned self-assembled monolayer. In oneexample of patterning the SAM for directed assembly of nanoscalecircuitry atomic force microscopy (AFM) is used to write, at highresolution, a pattern in SAM at which the SAM is removed. The patterncan be for example linear for parallel arrays, or a crossed array oflines linear in embodiments for making nanoscopic crossed arrays. Inanother technique, microcontact printing can be used to apply patternedSAM to the substrate. Next, open areas in the patterned surface (theSAM-free linear region between linear SAM) are filled with anamino-terminated SAM that interacts in a highly specific manner with ananowire such as a nanotube. The result is a patterned SAM, on asubstrate, including linear SAM portions separated by a line ofamino-terminated SAM material. Of course, any desired pattern can beformed where regions of the amino-terminated SAM material corresponds toregions at which wire deposition is desired. The patterned surface thenis dipped into a suspension of wires, e.g. nanotubes, and rinsed tocreate an array in which wires are located at regions of the SAM. Wherenanotubes are used, an organic solvent such as dimethyl formamide can beused to create the suspension of nanotubes. Suspension and deposition ofother nanowires is achievable with easily selected solvents.

Any of a variety of substrates and SAM-forming materials can be usedalong with microcontact printing techniques, such as those described inInternational Patent Publication WO 96/29629 of Whitesides, et al.,published Jun. 26, 1996 and incorporated herein by reference. PatternedSAM surfaces can be used to direct a variety of nanowires or nanoscaleelectronic elements. SAM-forming material can be selected, with suitableexposed chemical functionality, to direct assembly of a variety ofelectronic elements. Electronic elements, including nanotubes, can bechemically tailored to be attracted specifically to specific,predetermined areas of a patterned SAM surface. Suitable functionalgroups include, but are not limited to SH, NH₃, and the like. Nanotubesare particularly suitable for chemical functionalization on theirexterior surfaces, as is well known.

Chemically patterned surfaces other than SAM-derivatized surfaces can beused, and many techniques for chemically patterning surfaces are known.Suitable exemplary chemistries and techniques for chemically patterningsurfaces are described in, among other places, International PatentPublication No. WO 97/34025 of Hidber, et al, entitled, “MicrocontactPrinting of Catalytic Colloids”, and U.S. Pat. Nos. 3,873,359;3,873,360; and 3,900,614, each by Lando, all of these documentsincorporated herein by reference. Another example of a chemicallypatterned surface is a micro-phase separated block copolymer structure.These structures provide a stack of dense lamellar phases. A cut throughthese phases reveals a series of “lanes” wherein each lane represents asingle layer. The block copolymer is typically an alternating block andcan provide varying domains by which to dictate growth and assembly of ananowire. Additional techniques are described in International PatentPublication No. WO 01/03208 published Jan. 11, 2001 by Lieber, et al.,incorporated herein by reference.

Chemical changes associated with the nanowires used in the invention canmodulate the properties of the wires and create electronic devices of avariety of types. Presence of the analyte can change the electricalproperties of the nanowire through electrocoupling with a binding agentof the nanowire. If desired, the nanowires can be coated with a specificreaction entity, binding partner or specific binding partner, chosen forits chemical or biological specificity to a particular analyte.

The reaction entity is positioned relative to the nanowire to cause adetectable change in the nanowire. The reaction entity may be positionedwithin 100 nanometers of the nanowire, preferably with in 50 nanometersof the nanowire, and more preferably with in 10 nanometers of thenanowire, and the proximity can be determined by those of ordinary skillin the art. In one embodiment, the reaction entity is positioned lessthan 5 nanometers from the nanoscopic wire. In alternative embodiments,the reaction entity is positioned with 4 nm, 3 nm, 2 nm, and 1 nm of thenanowire. In a preferred embodiment, the reaction entity is attached tothe nanowire through a linker.

As used herein, “attached to,” in the context of a species relative toanother species or to a surface of an article, means that the species ischemically or biochemically linked via covalent attachment, attachmentvia specific biological binding (e.g., biotin/streptavidin),coordinative bonding such as chelate/metal binding, or the like. Forexample, “attached” in this context includes multiple chemical linkages,multiple chemical/biological linkages, etc., including, but not limitedto, a binding species such as a peptide synthesized on a polystyrenebead, a binding species specifically biologically coupled to an antibodywhich is bound to a protein such as protein A, which is covalentlyattached to a bead, a binding species that forms a part (via geneticengineering) of a molecule such as GST or, which in turn is specificallybiologically bound to a binding partner covalently fastened to a surface(e.g., glutathione in the case of GST), etc. As another example, amoiety covalently linked to a thiol is adapted to be fastened to a goldsurface since thiols bind gold covalently. “Covalently attached” meansattached via one or more covalent bonds. E.g. a species that iscovalently coupled, via EDC/NHS chemistry, to a carboxylate-presentingalkyl thiol which is in turn attached to a gold surface, is covalentlyattached to that surface.

Another aspect of the invention involves an article comprising a sampleexposure region and a nanowire able to detect the presence of absence ofan analyte. The sample exposure region may be any region in closeproximity to the nanowire wherein a sample in the sample exposure regionaddresses at least a portion of the nanowire. Examples of sampleexposure regions include, but are not limited to, a well, a channel, amicrochannel, and a gel. In preferred embodiments, the sample exposureregion holds a sample proximate the nanowire, or may direct a sampletoward the nanowire for determination of an analyte in the sample. Thenanowire may be positioned adjacent to or within the sample exposureregion. Alternatively, the nanowire may be a probe that is inserted intoa fluid or fluid flow path. The nanowire probe may also comprise amicro-needle and the sample exposure region may be addressable by abiological sample. In this arrangement, a device that is constructed andarranged for insertion of a micro-needle probe into a biological samplewill include a region surrounding the micro-needle that defines thesample exposure region, and a sample in the sample exposure region isaddressable by the nanowire, and vice-versa. Fluid flow channels can becreated at a size and scale advantageous for use in the invention(microchannels) using a variety of techniques such as those described inInternational Patent Publication No. WO 97/33737, published Sep. 18,1997, and incorporated herein by reference.

In another aspect of the invention, an article may comprise a pluralityof nanowires able to detect the presence or absence of a plurality ofone or more analytes. The individual nanowires may be differentiallydoped as described above, thereby varying the sensitivity of eachnanowire to the analyte. Alternatively, individual nanowires may beselected based on their ability to interact with specific analytes,thereby allowing the detection of a variety of analytes. The pluralityof nanowires may be randomly oriented or parallel to one another.Alternatively, the plurality of nanowires may be oriented in an array ona substrate.

FIG. 1 a shows one example of an article of the present invention. InFIG. 1 a, nanoscale detector device 10 is comprised of a single nanowire38 positioned above upper surface 18 of substrate 16. Chip carrier 12has an upper surface 14 for supporting substrate 16 and electricalconnections 22. Chip carrier 12, may be made of any insulating materialthat allows connection of electrical connections 22 to electrodes 36. Ina preferred embodiment, the chip carrier is an epoxy. Upper surface 14of the chip carrier, may be of any shape including, for example, planar,convex, and concave. In a preferred embodiment, upper surface 14 of thechip carrier is planar.

As shown in FIG. 1 a, lower surface of 20 of substrate 16 is positionedadjacent to upper surface 14 of the chip carrier and supports electricalconnection 22. Substrate 16 may typically be made of a polymer, silicon,quartz, or glass, for example. In a preferred embodiment, the substrate16 is made of silicon coated with 600 nm of silicon oxide. Upper surface18 and lower surface 20 of substrate 16 may be of any shape, such asplanar, convex, and concave. In a preferred embodiment, lower surface 20of substrate 16 contours to upper surface 14 of chip carrier 12.Similarly, mold 24 has an upper surface 26 and a lower surface 28,either of which may be of any shape. In a preferred embodiment, lowersurface 26 of mold 24 contours to upper surface 18 of substrate 16.

Mold 24 has a sample exposure region 30, shown here as a microchannel,having a fluid inlet 32 and fluid outlet 34, shown in FIG. 1 a on theupper surface 26 of mold 24. Nanowire 38 is positioned such that atleast a portion of the nanowire is positioned within sample exposureregion 30. Electrodes 36 connect nanowire 38 to electrical connection22. Electrical connections 22 are, optionally, connected to a detector(not shown) that measures a change in an electrical, or other propertyof the nanowire. FIGS. 3 a and 3 b are low and high resolution scanningelectron micrographs, respectively, of one embodiment of the presentinvention. A single silicon nanowire 38 is connected to two metalelectrodes 36. FIG. 7 shows an atomic force microscopy image of atypical SWNT positioned with respect to two electrodes. As seen in FIG.7, the distance between electrodes 36 is about 500 nm. In certainpreferred embodiments, electrode distances will range from 50 nm toabout 20000 nm 1, more preferably from about 100 nm to about 10000 nm,and most preferably from about 500 nm to about 5000 nm.

Where a detector is present, any detector capable of determining aproperty associated with the nanowire can be used. The property can beelectronic, optical, or the like. An electronic property of the nanowirecan be, for example, its conductivity, resistivity, etc. An opticalproperty associated with the nanowire can include its emissionintensity, or emission wavelength where the nanowire is an emissivenanowire where emission occurs at a p-n junction. For example, thedetector can be constructed for measuring a change in an electronic ormagnetic property (e.g. voltage, current, conductivity, resistance,impedance, inductance, charge, etc.) can be used. The detector typicallyincludes a power source and a voltmeter or amp meter. In one embodiment,a conductance less than 1 nS can be detected. In a preferred embodiment,a conductance in the range of thousandths of a nS can be detected. Theconcentration of a species, or analyte, may be detected from less thanmicromolar to molar concentrations and above. By using nanowires withknown detectors, sensitivity can be extended to a single molecule. Inone embodiment, an article of the invention is capable of delivering astimulus to the nanowire and the detector is constructed and arranged todetermine a signal resulting from the stimulus. For example, a nanowireincluding a p-n junction can be delivered a stimulus (electroniccurrent), where the detector is constructed and arranged to determine asignal (electromagnetic radiation) resulting from the stimulus. In suchan arrangement, interaction of an analyte with the nanowire, or with areaction entity positioned proximate the nanowire, can affect the signalin a detectable manner. In another example, where the reaction entity isa quantum dot, the quantum dot may be constructed to receiveelectromagnetic radiation of one wavelength and emit electromagneticradiation of a different wavelength. Where the stimulus iselectromagnetic radiation, it can be affected by interaction with ananalyte, and the detector can detect a change in a signal resultingtherefrom. Examples of stimuli include a constant current/voltage, analternating voltage, and electromagnetic radiation such as light.

In one example, a sample, such as a fluid suspected of containing ananalyte that is to be detected and/or quantified, e.g. a specificchemical contacts nanoscopic wire 38 having a corresponding reactionentity at or near nanoscopic wire 38. An analyte present in the fluidbinds to the corresponding reaction entity and causes a change inelectrical properties of the nanowire that is detected, e.g. usingconventional electronics. If the analyte is not present in the fluid,the electrical properties of the nanowire will remain unchanged, and thedetector will measure a zero change. Presence or absence of a specificchemical can be determined by monitoring changes, or lack thereof, inthe electrical properties of the nanowire. The term “determining” refersto a quantitative or qualitative analysis of a species via,piezoelectric measurement, electrochemical measurement, electromagneticmeasurement, photodetection, mechanical measurement, acousticmeasurement, gravimetric measurement and the like. “Determining” alsomeans detecting or quantifying interaction between species, e.g.detection of binding between two species.

Particularly preferred flow channels 30 for use in this invention are“microchannels”. The term microchannel is used herein for a channelhaving dimensions that provide low Reynolds number operation, i.e., forwhich fluid dynamics are dominated by viscous forces rather thaninertial forces. Reynolds number, sometimes referred to the ratio ofinertial forces to viscous forces is given as:Re=ρd ² /ητ+ρud/ηwhere u is the velocity vector, ρ is the fluid density, η is theviscosity of the fluid, d is the characteristic dimension of thechannel, and τ is the time scale over which the velocity is changing(where u/τ=δu/dt). The term “characteristic dimension” is used hereinfor the dimension that determines Reynolds number, as is known in theart. For a cylindrical channel it is the diameter. For a rectangularchannel, it depends primarily on the smaller of the width and depth. Fora V-shaped channel it depends on the width of the top of the “V”, and soforth. Calculation of Re for channels of various morphologies can befound in standard texts on fluid mechanics (e.g. Granger (1995) FluidMechanics, Dover, N.Y.; Meyer (1982) Introduction to Mathematical FluidDynamics, Dover, N.Y.).

Fluid flow behavior in the steady state (τ→infinity) is characterized bythe Reynolds number, Re=ρud/η. Because of the small sizes and slowvelocities, microfabricated fluid systems are often in the low Reynoldsnumber regime (Re less than about 1). In this regime, inertial effects,that cause turbulence and secondary flows, and therefore mixing withinthe flow, are negligible and viscous effects dominate the dynamics.Under these conditions, flow through the channel is generally laminar.In particularly preferred embodiments, the channel with a typicalanalyte-containing fluid provides a Reynolds number less than about0.001, more preferably less than about 0.0001.

Since the Reynolds number depends not only on channel dimension, but onfluid density, fluid viscosity, fluid velocity and the timescale onwhich the velocity is changing, the absolute upper limit to the channeldiameter is not sharply defined. In fact, with well designed channelgeometries, turbulence can be avoided for R<100 and possibly for R<1000,so that high throughput systems with relatively large channel sizes arepossible. The preferred channel characteristic dimension range is lessthan about 1 millimeter, preferably less than about 0.5 mm, and morepreferably less than about 200 microns.

In one embodiment, the sample exposure region, such as a fluid flowchannel 30 may be formed by using a polydimethyl siloxane (PDMS) mold.Channels can be created and applied to a surface, and a mold can beremoved. In certain embodiments, the channels are easily made byfabricating a master by using photolithography and casting PDMS on themaster, as described in the above-referenced patent applications andinternational publications. Larger-scale assembly is possible as well.

FIG. 1 b shows an alternative embodiment of the present inventionwherein the nanoscale detector device 10 of FIG. 1 a further includesmultiple nanowires 38 a-h (not shown). In FIG. 1 b, wire interconnects40 a-h connect corresponding nanowires 38 a-h to electrical connections22 a-h, respectively (not shown). In a preferred embodiment, eachnanowire 38 a-h has a unique reaction entity selected to detect adifferent analytes in the fluid. In this way, the presence or absence ofseveral analytes may be determined using one sample while performing onetest.

FIG. 2 a schematically shows a portion of a nanoscale detector device inwhich the nanowire 38 has been modified with a reactive entity that is abinding partner 42 for detecting analyte 44. FIG. 2 b schematicallyshows a portion of the nanoscale detector device of FIG. 2 a, in whichthe analyte 44 is attached to the specific binding partner 42.Selectively functionalizing the surface of nanowires can be done, forexample, by functionalizing the nanowire with a siloxane derivative. Forexample, a nanowire may be modified after construction of the nanoscaledetector device by immersing the device in a solution containing themodifying chemicals to be coated. Alternatively, a micro-fluidic channelmay be used to deliver the chemicals to the nanowires. For example,amine groups may be attached by first making the nanoscale detectordevice hydrophilic by oxygen plasma, or an acid and/or oxidizing agentand the immersing the nanoscale detector device in a solution containingamino silane. By way of example, DNA probes may be attached by firstattaching amine groups as described above, and immersing the modifiednanoscale detector device in a solution containing bifunctionalcrosslinkers, if necessary, and immersing the modified nanoscaledetector device in a solution containing the DNA probe. The process maybe accelerated and promoted by applying a bias voltage to the nanowire,the bias voltage can be either positive or negative depending on thenature of reaction species, for example, a positive bias voltage willhelp to bring negatively charged DNA probe species close to the nanowiresurface and increase its reaction chance with the surface amino groups.

FIG. 4 a schematically shows another embodiment of a nanoscale sensorhaving a backgate 46. FIG. 4 b shows conductance vs. time at with abackgate voltage ranging from −10V to +10V. FIG. 4 c shows conductancevs. backgate voltage. The backgate can be used to inject or withdraw thecharge carriers from the nanowire. Therefore, it may be used to controlthe sensitivity and the dynamic range of the nanowire sensor and to drawanalytes to the nanowire.

FIGS. 5 a and 5 b show the conductance for a single silicon nanowire,native and coated, respectively, as a function of pH. As seen in FIG. 4,the conductance of the silicon nanowire changes from 7 to 2.5 when thesample is changed. The silicon nanowire of FIG. 5 has been modified toexpose amine groups at the surface of the nanowire. FIG. 5 shows achange in response to pH when compared to the response in FIG. 4. Themodified nanowire of FIG. 5 shows a response to milder conditions suchas, for example, those present in physiological conditions in blood.

FIG. 6 shows the conductance for a silicon nanowire having a surfacemodified with an oligonucleotide agent reaction entity. The conductancechanges dramatically where the complementary oligonucleotide analytebinds to the attached oligonucleotide agent.

FIG. 8 a shows the change in the electrostatic environment with changein gate voltage for a single-walled nanotube. FIGS. 8 b and c, show thechange in conductance induced by the presence of NaCL and CrClx of asingle-walled carbon nanotube.

FIG. 9 a shows the change in conductance as nanosensors with hydroxylsurface groups are exposed to pH levels from 2 to 9. FIG. 9 b shows thechange in conductance as nanosensors modified with amine groups areexposed to pH levels from 2 to 9. FIG. 9 c show the relative conductanceof the nanosensors with changes in pH levels. The results showed alinear response in a wide range of pH, which clearly demonstrated thedevice is suitable for measuring or monitoring pH conditions of aphysiological fluid.

FIG. 10 a shows an increase in conductance of a silicon nanowire(SiNW)modified with a reaction entity BSA Biotin, as it is exposed first to ablank buffer solution, and then to a solution containing an analyte, 250nM Streptavidin. FIG. 10 b shows an increase in conductance of a SiNWmodified with BSA Biotin, as it is exposed first to a blank buffersolution, and then to a solution containing 25 pM Streptavidin. FIG. 10c shows no change in conductance of a bare SiNW as it is exposed firstto a blank buffer solution, and then to a solution containingStreptavidin. FIG. 10 d shows the conductance of a SiNW modified withBSA Biotin, as it is exposed to a buffer solution, and then to asolution containing d-biotin Streptavidin. FIG. 10 e shows the change inconductance of a Biotin modified nanosensor exposed to a blank buffersolution, then to a solution containing Streptavidin, and then again toa blank buffer solution. Replacing Streptavidin with the blank bufferdoes not change the conductance, indicating that the Streptavidin hasirreversibly bound to the BSA Biotin modified nanosensor. FIG. 10 fshows no change in conductance of a bare SiNW as it is alternatelyexposed to a buffer solution and a solution containing streptavidin.These results demonstrate the nanowire sensor is suitable for specificdetection of bio-markers at very high sensitivity.

FIG. 11 a shows a decrease in conductance of a BSA-Biotin modified SiNWas it is exposed first to a blank buffer solution, then to a solutioncontaining antibiotin. The conductance then increases upon replacing thesolution containing antibiotin with a blank buffer solution, and thenagain decreases upon exposing the nanosensor to a solution containingantibiotin. FIG. 11 a indicates a reversible binding between biotin andantibiotin. FIG. 11 b shows the conductance of a bare SiNW duringcontact with a buffer solution and then a solution containingantibiotin. FIG. 11 c shows the change in conductance of a BSA-Biotinmodified SiNW during exposure to a buffer, other IgG type antibodies,and then antibiotin, an IgGI type antibody to biotin. FIG. 11 cindicates that the BSA biotin modified SiNW detects the presence ofantibiotin, without being hindered by the presence of other IgG typeantibodies. These results demonstrate the potential of the nanowiresensor for dynamic bio-marker monitoring under a real physiologicalcondition.

Amine modified SiNW may also detect the presence of metal ions. FIG. 12a shows the change in conductance of an amine modified SiNW whenalternately exposed to a blank buffer solution and a solution containing1 mM Cu(II). FIG. 12 b shows the increases in conductance as the aminemodified SiNW is exposed to concentrations of Cu(II) from 0.1 mM to 1mM. FIG. 12 c shows the increase in conductance verses Cu(II)concentration. FIG. 12 d shows no change in conductance of an unmodifiedSiNW when exposed first to a blank buffer solution and then to 1 mMCu(II). FIG. 12 e shows no change in the conductance of an aminemodified SiNW when exposed first to a blank buffer solution and then to1 mM Cu(II)-EDTA, wherein the EDTA interferes with the ability of Cu(II)to bind to the modified SiNW. These results demonstrate the potential ofthe nanowire sensor for use in inorganic chemical analysis.

FIG. 13 a shows the conductance of a silicon nanowire modified withcalmodulin, a calcium binding protein. In FIG. 13 a, region 1 shows theconductance of the calmodulin modified silicon when exposed to a blankbuffer solution. Region 2 shows the drop in conductance of the samenanowire when exposed to a solution containing calcium ions noted inFIG. 3 with a downward arrow. Region 3 shows the increase in conductanceof the same nanowire is again contacted with a blank buffer solution,indicated with an upward arrow. The subsequent return of conductance toits original level indicates that the calcium ion is reversible bound tothe calmodulin modified nanowire. FIG. 13 b shows no change inconductance of an unmodified nanowire when exposed first to a blankbuffer solution, and then to a solution containing calcium ions.

As indicated by the disclosure above, in one embodiment, the inventionprovides a nanoscale electrically based sensor for determining thepresence or absence of analytes suspected of being present in a sample.The nanoscale provides greater sensitivity in detection than thatprovided by macroscale sensors. Moreover, the sample size used innanoscale sensors is less than or equal to about 10 microliters,preferably less than or equal to about 1 microliter, and more preferablyless than or equal to about 0.1 microliter. The sample size may be assmall as about 10 nanoliters or less. The nanoscale sensor also allowsfor unique accessibility to biological species and may be used both invivo and in vitro applications. When used in vivo, the nanoscale sensorand corresponding method result in a minimally invasive procedure.

FIG. 14 a shows a calculation of sensitivity for detecting up to 5charges compared to the doping concentration and nanowire diameter. Asindicated, the sensitivity of the nanowire may be controlled by changingthe doping concentration or by controlling the diameter of the nanowire.For example, increasing the doping concentration of a nanowire increasesthe ability of the nanowire to detect more charges. Also, a 20 nm wirerequires less doping than a 5 nm nanowire for detecting the same numberof charges. FIG. 14 b shows a calculation of a threshold doping densityfor detecting a single charge compared to the diameter of a nanowire.Again, a 20 nm nanowire requires less doping than a 5 nm nanowire todetect a single charge.

FIG. 15 a shows a schematic view of an InP nanowire. The nanowire may behomogeneous, or may comprise discrete segments of n and p type dopants.FIG. 15 b shows the change in luminescence of the nanowire of 15 a overtime as pH is varied. As indicated, the intensity of the light emissionof a nanowire changes relative to the level of binding. As the pHincreases, the light intensity drops, and as the pH decreases, the lightintensity increases. One embodiment of the invention contemplatesindividually addressed light signal detection by sweeping through eachelectrode in a microarray. Another embodiment of the inventioncontemplates a two signal detector, such as, an optical sensor combinedwith an electrical detector.

FIG. 16 a depicts one embodiment of a nanowire sensor. As show in FIG.16 a, the nanowire sensor of the invention comprises a single moleculeof doped silicon 50. The doped silicon is shaped as a tube, and thedoping can be n-doped or p-doped. Either way, the doped silicon nanowireforms a high resistance semiconductor material across which a voltagemay be applied. The exterior surface and the interior surface of thetube will have an oxide formed thereon and the surface of the tube canact as the gate 52 of an FET device and the electrical contacts ateither end of the tube allow the tube ends to acts as the drain 56 andthe source 58. In the depicted embodiment the device is symmetric andeither end of the device may be considered the drain or the source. Forpurpose of illustration, the nanowire of FIG. 16 a defines the left-handside as the source and the right hand side as the drain. FIG. 16 a alsoshow that the nanowire device is disposed upon and electricallyconnected to two conductor elements 54.

FIGS. 16 a and 16 b illustrate an example of a chemical/or ligand-gatedField Effects Transistor (FET). FETs are well know in the art ofelectronics. Briefly, a FET is a 3-terminal device in which a conductorbetween 2 electrodes, one connected to the drain and one connected tothe source, depends on the availability of charge carriers in a channelbetween the source and drain. FETs are described in more detail in TheArt of Electronics, Second Edition by Paul Horowitz and Winfield Hill,Cambridge University Press, 1989, pp. 113-174, the entire contents ofwhich is hereby incorporated by reference. This availability of chargecarriers is controlled by a voltage applied to a third “controlelectrode” also know as the gate electrode. The conduction in thechannel is controlled by a voltage applied to the gate electrode whichproduces an electric field across the channel. The device of FIGS. 16 aand 16 b may be considered a chemical or ligand-FET because the chemicalor ligand provides the voltage at the gate which produced the electricfield which changes the conductivity of the channel. This change inconductivity in the channel effects the flow of current through thechannel. For this reason, a FET is often referred to as atransconductant device in which a voltage on the gate controls thecurrent through the channel through the source and the drain. The gateof a FET is insulated from the conduction channel, for example, using asemi conductor junction such in a junction FET (JFET) or using an oxideinsulator such as in a metal oxide semiconductor FET (MOSFET). Thus, inFigures A and B, the SIO2 exterior surface of the nanowire sensor mayserve as the gate insulation for the gate.

In application, the nanowire device illustrated in Figure A provides anFET device that may be contacted with a sample or disposed within thepath of a sample flow. Elements of interest within the sample cancontact the surface of the nanowire device and, under certainconditions, bind or otherwise adhere to the surface.

To this end the exterior surface of the device may have reactionentities, e.g., binding partners that are specific for a moiety ofinterest. The binding partners will attract the moieties or bind to themoieties so that moieties of interest within the sample will adhere andbind to the exterior surface of the nanowire device. An example of thisis shown in FIG. 16 c where there is depicted a moiety of interest 60(not drawn to scale) being bound to the surface of the nanowire device.

Also shown, with reference to FIG. 16 c, that as the moieties build up,a depletion region 62 is created within the nanowire device that limitsthe current passing through the wire. The depletion region can bedepleted of holes or electrons, depending upon the type of channel. Thisis shown schematically in FIG. 16 d below. The moiety has a charge thatcan lead to a voltage difference across the gate/drain junction.

A nanoscale sensor of the present invention can collect real time data.The real time data may be used, for example, to monitor the reactionrate of a specific chemical or biological reaction. Physiologicalconditions or drug concentrations present in vivo may also produce areal time signal that may be used to control a drug delivery system. Forexample, the present invention includes, in one aspect, an integratedsystem, comprising a nanowire detector, a reader and a computercontrolled response system. In this example, the nanowire detects achange in the equilibrium of an analyte in the sample, feeding a signalto the computer controlled response system causing it to withhold orrelease a chemical or drug. This is particularly useful as animplantable drug or chemical delivery system because of its small sizeand low energy requirements. Those of ordinary skill in the art are wellaware of the parameters and requirements for constructing implantabledevices, readers, and computer-controlled response systems suitable foruse in connection with the present invention. That is, the knowledge ofthose of ordinary skill in the art, coupled with the disclosure hereinof nanowires as sensors, enables implantable devices, real-timemeasurement devices, integrated systems, and the like. Such systems canbe made capable of monitoring one, or a plurality of physiologicalcharacteristics individually or simultaneously. Such physiologicalcharacteristics can include, for example, oxygen concentration, carbondioxide concentration, glucose level, concentration of a particulardrug, concentration of a particular drug by-product, or the like.Integrated physiological devices can be constructed to carry out afunction depending upon a condition sensed by a sensor of the invention.For example, a nanowire sensor of the invention can sense glucose leveland, based upon the determined glucose level can cause the release ofinsulin into a subject through an appropriate controller mechanism.

In another embodiment, the article may comprise a cassette comprising asample exposure region and a nanowire. The detection of an analyte in asample in the sample exposure region may occur while the cassette isdisconnected to a detector apparatus, allowing samples to be gathered atone site, and detected at another. The cassette may be operativelyconnectable to a detector apparatus able to determine a propertyassociated with the nanowire. As used herein, a device is “operativelyconnectable” when it has the ability to attach and interact with anotherapparatus.

In another embodiment, one or more nanowires may be positioned in amicrofluidic channel. One or more different nanowires may cross the samemicrochannel at different positions to detect a different analyte or tomeasure flow rate of the same analyte. In another embodiment, one ormore nanowires positioned in a microfluidic channel may form one of aplurality of analytic elements in a micro needle probe or a dip and readprobe. The micro needle probe is implantable and capable of detectingseveral analytes simultaneously in real time. In another embodiment, oneor more nanowires positioned in a microfluidic channel may form one ofthe analytic elements in a microarray for a cassette or a lab on a chipdevice. Those skilled in the art would know such cassette or lab on achip device will be in particular suitable for high throughout chemicalanalysis and combinational drug discovery. Moreover, the associatedmethod of using the nanoscale sensor is fast and simple, in that it doesnot require labeling as in other sensing techniques. The ability toinclude multiple nanowires in one nanoscale sensor, also allows for thesimultaneous detection of different analytes suspected of being presentin a single sample. For example, a nanoscale pH sensor may include aplurality of nanoscale wires that each detect different pH levels, or ananoscale oligo sensor with multiple nanoscale wires may be used todetect multiple sequences, or combination of sequences.

Those skilled in the art would readily appreciate that all parameterslisted herein are meant to be exemplary and that actual parameters willdepend upon the specific application for which the methods and apparatusof the present invention are used. It is, therefore, to be understoodthat the foregoing embodiments are presented by way of example only andthat, within the scope of the appended claims and equivalents thereto,the invention may be practiced otherwise than as specifically described.

1. An article comprising: a semiconductor nanowire comprising a coreregion and an outer region surrounding the core region, wherein theouter region is selectively functionalized with a chemical or biologicalspecies added to the nanowire after construction of the nanowire.
 2. Thearticle as in claim 1, wherein the semiconductor nanowire is a siliconnanowire.
 3. The article as in claim 1, wherein the core region of thenanowire has a diameter ranging from 0.5 nm to 200 nm.
 4. The article asin claim 1, wherein the outer region is selectively functionalized withone or more of a metallic element, an oxide, a sulfide, a nitride, aselenide, a polymer, or a polymer gel.
 5. The article as in claim 1,wherein the outer region is selectively functionalized with one or moreof —OH, —CHO, —COOH, —SO₃H, —CN, —NH₂, —SH, —COSH, —COOR, or a halide.6. The article as in claim 1, wherein the outer region is selectivelyfunctionalized with one or more of a nucleic acid, an antibody, anantigen, a sugar, a carbohydrate, an amino acid, a protein, or anenzyme.
 7. The article as in claim 1, wherein the outer region comprisesa reaction entity positioned relative to the nanowire such that aninteraction between the reaction entity and an analyte in a samplecauses a detectable change in a property of the nanowire.
 8. The articleas in claim 1, further comprising a detector constructed and arranged todetermine a property associated with the nanowire.
 9. The article as inclaim 8, wherein the detector is constructed and arranged to determinean electrical property associated with the nanowire.
 10. The article asin claim 1, wherein the chemical or biological species is attached tothe nanowire through a linker.
 11. An article comprising: asemiconductor nanowire comprising a core region and an outer region,wherein the outer region comprises functional moieties forming a coatingon the core region, at least some of which functional moieties have achemical or biological species attached thereto.
 12. The article as inclaim 11, wherein the semiconductor nanowire is a silicon nanowire. 13.The article as in claim 11, wherein the core region of the nanowire hasa diameter ranging from 0.5 nm to 2,00 nm.
 14. The article as in claim11, wherein the functional moieties include one or more of —OH, —CHO,—COOH, —SO₃H, —CN, —NH₂, —SH, —COSH, —COOR, or a halide.
 15. The articleas in claim 11, wherein the functional moieties include one or more of anucleic acid, an antibody, an antigen, a sugar, a carbohydrate, an aminoacid, a protein, or an enzyme.
 16. The article as in claim 11, whereinat least one of the chemical or biological species is a nucleic acid, anantibody, an antigen, a sugar, a carbohydrate, an amino acid, a protein,or an enzyme.
 17. The article as in claim 11, further comprising adetector constructed and arranged to determine a property associatedwith the nanowire.
 18. The article as in claim 17, wherein the detectoris constructed and arranged to determine an electrical propertyassociated with the nanowire.